1. Field of the Invention
This invention relates to a process for separating entrained organic fluids from gaseous streams in a coal deashing system utilizing an ash concentrate produced by the system while operating at elevated temperatures and pressures.
2. Description of the Prior Art
Heretofore, coal has been mixed with certain solvents at elevated temperatures and pressures to produce mixtures of dissolved and undissolved coal. Various systems have been proposed for separating the dissolved coal from the undissolved coal.
In U.S. Pat. No. 4,244,812, assigned to the same assignee as the present invention, an improved system is disclosed for effecting such a separation.
In that system, a feed mixture comprising soluble coal products, solvent and insoluble coal products is separated in a first separation zone maintained at an elevated temperature and pressure into a first light fraction and a first heavy fraction comprising insoluble coal products and some solvent. The first heavy fraction also includes a small quantity of relatively low melting point soluble coal products such as coal tars that are dissolved in the solvent. The insoluble coal products comprise the undissolved coal, mineral matter, other solid inorganic particulate matter and other such matter which is insoluble in the solvent solution under the operating conditions of the process.
The first heavy fraction is withdrawn from the first separation zone and the pressure level is reduced at least about 100 psig. and preferably at least about 500 psig. to vaporize the solvent and yield the insoluble coal products in a relatively dry, powdery form referred to as "ash concentrate." Upon the vaporization of the solvent from the first heavy phase, a portion of the formerly soluble coal tars and other organic fluids separate from the remainder of the heavy phase and are entrained in the vaporized solvent in the form of a fog or atomized mist. The flashed heavy phase then is introduced into another separation zone, such as for example, a cyclone or gravity settler, to separate the ash concentrate from the vaporized solvent. The vaporized solvent is passed from this separation zone through a withdrawal conduit for recycle in the process. Since the organic fluids are at a temperature near to or above their melting point, they exhibit a highly viscous behavior and tend to deposit upon and adhere to the inside of the solvent withdrawal conduit. In some instances a small quantity of the fine particles of ash concentrate also are entrained in the withdrawn solvent stream together with the entrained organic fluids. If the relatively dry ash concentrate contacts the coating of organic fluids within the solvent withdrawal conduit, it can adhere to the coating. An agglomerate can form through continued collection of organic fluids and ash concentrate which will block the solvent withdrawal conduit. The formation of such a blockage requires termination of process operation to permit removal of the agglomerate. A tedious and expensive cleanout then is required to restore operation.
It would be desirable to provide a method by which the blockage problem associated with the separation of the solvent from the first heavy fraction withdrawn from the first separation zone can be alleviated.